Conventionally, various kinds of natural stones and artificial marbles (hereinafter referred to as just “stone material”) are usually cut out from a slab material 20–40 mm in thickness and 1500–2000 mm long on its side as a square slab plate 70 shown in FIG. 7. When constructing as floor material or wall material on a construction site, a desired area is obtained by bonding their edges 71 together. To bond together stone materials heavy and extremely hard and brittle firmly through a side face having a small bonding area, various devices have been made. For example, as a method easy to apply on a construction site and reliable, a method in which a groove 72 is formed in the side faces to be bonded together and the side faces 71 containing the groove 72 are coated with glue 73 mainly composed of epoxy base resin, polyester base resin and the like and bonded together has been widely adopted (see FIG. 8).
According to the above-described method, by forming the groove in each of the edges faces of the stone materials to be bonded together, the bonding area can be increased and further, glues applied in two grooves merge with each other so as to obtain strict bonding condition. The adhesiveness of the glue supplements the brittleness of the bonding faces of the hard, brittle materials. Further, if the thickness of the stone materials are different, the groove under the above-described method acts as a role as a construction criterion. Thus, it is preferable that the grooves formed in the bonding faces oppose each other accurately while their depths are balanced to a specified one.
The groove for glue formed in the above-mentioned slab plate is generally formed in the width of 4–5 mm and the depth of 7–12 mm and as described above, to intensify the bonding strength, balances of the opposing position and the width and depth of the groove and the like are important factors. However as regards a groove cutting means for a stone material on a construction site, currently, a disc type cutter used for mainly cutting a stone material and the like or an offset type cutter having a concave face in the center of its substrate is employed, and individual worker works manually relying upon his experience using such a handy electric tool. If taking up an extreme example, some worker uses two pieces of diamond saw blades such that they overlap in order to obtain a width of the groove (of course, this is an illegal use), indicating that the cutting depends on the degree of skill accumulated in the worker for a long time.
Upon use, the aforementioned disc cutter or the offset cutter is attached to a handy electric tool which rotates at high speeds such as a grinder and sander. A deflection originating from vibration accompanying the rotation of the electric tool and a distortion of the substrate of the cutter provide a large disturbance on accurate cutting in a cutting object material and additionally, a large burden is born on a worker. Thus, according to an offset type cutter (for example, Japanese Patent Application Laid-Open No. 2002-103235) which has been proposed to solve the problems and used actually, in a rotary cutting tool (for example, Japanese Patent Application Laid-Open No. HEI7-276215) which absorbs vibration and deflection by interposing an elastic body between the cutter blade and spindle or an offset cutter in which a plurality of ultra abrasive layers are formed on the outer periphery of its substrate, by forming ultra abrasive layer by pressurizing at least a portion near the outer periphery of a drawn substrate with a die and sintering, distortion of the substrate is eliminated by sintering so that vibration originating therefrom is reduced.